QUOTE: When an English speaker says "America," in the singular form, they're referring to the United States of America. That usage of the term is fairly new. As recently as the 1950s, the name America usually referred to a single continent that included both North and South America. Leading up to WWII, it served US geopolitical interests to represent America as a unified Western Hemisphere landmass that was entirely under US control. Then, during the early 1950s, almost all American geographers made a definitive case that, being visually distinct landmasses, North and South America should have separate designations.

https://online.seterra.com/en/p/america